1. Field of the Invention
The present invention relates to fluorinated photopolymers having a cross linking group and a photosensitizer incorporated into the polymer. Such photopolymers are particularly useful in organic electronic and bioelectronic devices.
2. Discussion of Related Art
Photocurable polymeric compositions have many possible commercial applications. They can be used as photoresists, dielectrics, insulators, semiconductors, encapsulants, inert overcoats, water or oil repellent layers, light blocking or emitting layers, paints, printing inks and the like. Certain photocurable polymeric compositions are of particular use in the fabrication of organic electronic devices, including bioelectronic devices.
Organic electronic devices may offer certain performance and price advantages relative to conventional inorganic-based devices. As such, there has been much commercial interest in the use of organic materials in electronic device fabrication. Specifically, organic materials such as conductive polymers can be used to manufacture devices that have reduced weight and drastically greater mechanical flexibility compared to conventional electronic devices based on metals and silicon. Further, devices based on organic materials are likely to be significantly less damaging to the environment than devices made with inorganic materials, since organic materials do not require toxic metals and can ideally be fabricated using relatively benign solvents and methods of manufacture. Thus, in light of these superior weight and mechanical properties, and particularly in light of the lowered environmental impact in fabrication and additionally in disposal, electronic devices based on organic materials are expected to be less expensive than devices based on conventional inorganic materials.
One problem facing bioelectronic and organic electronic devices is that the materials and patterning processes used for conventional inorganic electronics are often not compatible with biological and organic electronic materials. Thus, new patterning materials and processes are needed.
For example, although the use of photoresists is routine in the patterning of traditional electronic devices based on inorganic materials, photolithographic patterning has been difficult when applied to biological or organic electronic materials. Specifically, biological and organic electronic materials are often much less resistant to the solvents that are used for conventional photolithography, as well as to the intense light sources that are used in these processes, with the result that conventional lithographic solvents and processes tend to degrade bioelectronic and organic electronic devices. Although there have been various attempts to overcome these problems, e.g., by ink-jet printing or shadow mask deposition, these alternative methods do not produce the same results as would be obtained with successful photolithography. Specifically, neither ink-jet printing nor shadow mask deposition can achieve the fine pattern resolutions that can be obtained by conventional lithography.
US 2011/0159252 discloses a useful method for patterning organic electronic materials by an “orthogonal” process that uses fluorinated solvents and fluorinated photoresists. The fluorinated solvents have very low interaction with organic electronic materials
Although the orthogonal process has made good progress, these fluorinated systems do not always have sufficient sensitivity to typical exposing radiation, especially in the range of 300 to 450 nm. Conventional photoresist compositions may include a photosensitizing additive, commonly referred to as a sensitizer or sensitizing dye, to increase the photosensitivity of the photoresist at a particular wavelength. By varying the amount of sensitizer added to the photoresist, the photo speed and spectral sensitivity of the system can be modulated. An important technical limitation of most existing sensitizers is that they are not highly soluble in fluorinated coating solvents or fluorinated developing solutions. Consequently, the concentration of sensitizer that can be employed in fluorinated photoresist composition is very limited and development can leave behind a residue of the sensitizer. Secondly, some sensitizers are susceptible to sublimation during the baking process, thereby depleting the photoresist formulation of sensitizer. In addition, the sublimed sensitizer can coat the baking tools and then flake off during the subsequent processing, resulting in further problems in the system.
Electronic devices may require an insulating or dielectric layer (e.g., SiO2 or spin-coated polymers). Here again, typical insulating or dielectric materials are often not compatible with sensitive bioelectronic and organic electronic material layers. Further, if a dielectric photopolymer is sensitized with a small molecule sensitizer, the small molecule sensitizer might leach into the active organic or biological material and negatively impact device performance.
In light of the above, there is a need to provide a more effective sensitization of photopolymers, and in particular, photopolymers that are compatible in bioelectronic and organic electronic devices.